1. Field of the Invention
The subject invention relates to a system and method for processing signals, and more particularly, to signal conditioning circuitry for linear variable differential transformers (LVDT) and rotary variable differential transformers (RVDT).
2. Background of the Related Art
Displacement sensors that produce either digital or analog outputs are well known in the art. Analog output displacement sensors include variable resistors, capacitors in single-coil units, and multiple-coil inductive sensors. Digital output displacement sensors include the linear variable differential transformer (LVDT) and the rotary variable differential transformer (RVDT). These transformers include a moveable core having three windings which sense displacement. LVDTs and RVDTs are used to measure linear or angular displacement and are connected mechanically between the object being sensed and a reference object. The output voltage of the transformer is proportional to the displacement of the moveable core, and can be used to measure the motion or position of a reference object.
The linear variable differential transformer (LVDT) includes a movable magnetic core, a primary winding and two secondary windings. Since there is no contact between the core and the windings, there is no friction and no mechanical wear to limit the life of the transducer. This is especially important in high reliability applications and in hostile environments. As an example, the control surfaces of a fixed or rotary wing aircraft exhibit vibration which would quickly destroy a mechanical contact-type transducer. The position of the magnetic core determines the voltage induced on each of the two secondary windings. When the core is centered relative to the secondary windings, an equal voltage is induced on each secondary winding. This is the balanced or null position. As the core is displaced from the center, or null point, the voltage induced on one secondary winding increases while the voltage on the other secondary winding decreases. The two secondary windings are usually connected in series, and the resulting differential voltage is measured. The phase of the output voltage relative to the primary voltage indicates the direction of displacement relative to the null position. An RVDT sensor operates in a similar manner wherein the movable iron-core rotates about a fixed axis.
In the past, circuitry for converting a signal from an LVDT or RVDT sensor into a reliable output voltage included complex processing methodologies and components, as disclosed for example in U.S. Pat. No. 4,591,765 to McCorkle and U.S. Pat. No. 4,909,921 to DeVito. It would be beneficial therefore to provide a reliable system for conditioning LVDT and RVDT signals that employs relatively simple computational methodologies and relatively fewer and less complex components than prior art signal conditioning systems.